Respiratory Distress Syndrome of the newborn is a major cause of death in the neonate. This disorder is characterized by a lack of surfactant in the lungs. The hormones insulin, cortisol and thyroxin have been implicated as possible mediators of surfactant production. The effect of these hormones upon type II cells of fetal rat lung grown in vitro within an organotypic culture system will be tested. The effects of these hormones upon surfactant levels and synthesis will be measured as well as other parameters of general metabolism such as glucose consumption, lactate and CO2 production, protein synthesis, and fine structure. Organotypic cultures will be established from maturing (19 day) and immature (16 day) fetal rat lungs and maintained in culture for periods of up to 2 weeks. The cultures will be treated with various concentrations and combinations of the hormones insulin, cortisol and thyroxin for periods of 3 hours to several days. After hormone treatment the cultures will be examined for morphological changes. Cultures will also be incubated with either (U-14C) glucose (1-14C) palmitate or (Me-14C) choline and the incororation into a surfactant lipoprotein fraction measured. The surfactant material will be isolated by discontinuous sucrose density centrifugation and the phospholipids isolated and fractioned by established procedures. Alternatively following hormone treatment the type II cells will be incubated with (U-14C) glucose and the uptake of glucose measured. Lactate and CO2 production will also be measured in order to ascertain if hormonal treatment affects the glycolytic flux of the type II cells as it does in other cells either in vivo or in vitro.